US BATFE. 2021 ‘National Firearms Act Registered Weapons by State (May 2021).’ Firearms Commerce In The United States. Annual Statistical Update 2021. Washington DC: US Department of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). 1 January

Relevant contents

Machinegun (3): 741,146
Short Barreled Rifle (5) 532,725
Short Barreled Shotgun (6) 162,267
Total 1,436,138

(3) Machinegun is defined as any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person.

(5) Short-barreled rifle is defined as a rifle having one or more barrels less than 16 inches in length, and any weapon made from a rifle, whether by alteration, modification, or otherwise, if such weapon, as modified, has an overall length of less than 26 inches.

(6) Short-barreled shotgun is defined as a shotgun having one or more barrels less than 18 inches in length, and any weapon made from a shotgun, whether by alteration, modification, or otherwise, if such weapon as modified has an overall length of less than 26 inches.

Last accessed at:
https://www.atf.gov/file/160581/download